Test equipment plays a vital role in many technical areas. For example, optical communications component manufacturers have to conduct tests on their products during manufacture to ensure each product is compliant with desired specifications.
As communication rates and requirements placed on communications equipment increase, so do the demands on test equipment. For example, in optical communication systems have transmission rates on the order of Gb/s and bit error rates (BER) on the order of 10−12, the demands placed on the sensitivity and reliability of test equipment continues to increase. In addition to measuring parameters such as transmitted power and receiver sensitivity, test equipment is often relied upon for measuring the quality of digital transmissions. For example, the test equipment may be relied on to measure rise times, jitter, noise and chirp, to mention only a few.
As mentioned, the accuracy and reliability of measurements made with test equipment is of major concern in many technical areas. In an attempt to improve the accuracy of test equipment, calibration of the test equipment is carried out. The calibration of the test equipment is normally carried our in accordance with one or more requirements of a standards body. For example, the calibration standards may be in accordance with the National Institute of Science and Technology (NIST). These calibrations procedures are often carried out prior to shipment of the equipment to the customer and at periodic intervals thereafter. This recalibration is necessary to maintain the measurement quality, because it is possible that components within the test apparatus “drift” with time.
While calibration and recalibration of test equipment is important, in many instances, it is difficult for the user of the test equipment to know if the equipment remains calibrated after receipt from the manufacture or use. Thus, the test equipment may be unreliable. For example, the test equipment may have been affected during shipping or after being used for some time, or both; or the equipment may have been subjected to environmental stresses. Thus, the user of equipment may believe that the test equipment is functioning within specified limits of calibration, when in reality it is not.
As can be readily appreciated, the accuracy and reliability of test equipment over time can degrade without detection by the user. Thus, there is a need for test equipment that overcomes at least the shortcomings described above.